Many prior art systems for numerically controlling machine tools have been proposed. Some of these systems have been built and are presently being used to control various types of machine tools. In general, the more modern prior art machine tool control systems, regardless of whether or not they have been built and used, include feedback servo loops for controlling the position of cutters and/or parts, depending upon whether the cutter, part or both are to be moved during the machining (e.g., cutting) operation. Normally, a feedback servo control loop is provided for each controlled axis of movement. The feedback servo loops compare program position signals for the relevant axis with the sensed position of the machine tool along that axis. Any deviation therebetween creates an error signal that is used to control movement of the part or cutter along the axis in the direction that reduces the error signal to zero. In some prior art systems, the rate of movement along the relevant axis is controlled or limited to minimize overshoot; and, thus, part cutting errors caused by overshoot.
While, as noted above, many prior art machine tool control systems have been built and are in use, such systems have a number of disadvantages. Ideally, the part and/or cutter movement mechanisms of a machine tool will function exactly as designed. However, because these components are mechanical, such a result does not occur. More specifically, because the mechanisms for moving cutters and/or parts are mechanical, even when new, they deviate to some degree from their design parameters. Similarly, servo and other mechanical control mechanisms do not function exactly in accordance with their design parameters, even when new. And, of course, as a machine tool is used its parts wear, whereby the operation of the mechanical mechanisms of the machine change. Servo control loops and part movement mechanisms, e.g., electrical and hydraulic systems for moving cutters and/or parts also change with time as a result of part wear and deterioration. In other words, even when new, the transfer function of machine tool elements if not ideal. That is, the response of the machine tool elements to an input stimuli (i.e., the transfer function) is not ideal. Moreover, the transfer function changes with machine use. The transfer function also changes each time a machine tool element is repaired, adjusted or replaced. The end result of transfer function changes have been twofold. First, machine tools have been relatively frequently adjusted to reduce the effects of wear. Secondly, parts produced by numerically controlled machines have been inspected to determine whether or not they fall within allowable tolerances. Such post process inspection is very costly and time consuming, particularly when the part must meet stringent tolerance requirements.
Therefore, it is an object of this invention to provide a new and improved machine tool controller.
It is another object of this invention to provide a machine tool controller and part inspection monitor suitable for controlling a machine tool and providing a readout indicating when the shape and/or size of an actual part deviates from the shape and/or size of the desired part.
It is a still further object of this invention to provide a machine tool controller that continuously determines the transfer function of a machine tool and uses the transfer function information in a manner that automatically compensates for machine tool wear so as to substantially reduce the need to frequently adjust the machine tool or replace parts thereof to compensate for such wear.
It is yet a further object of this invention to provide a machine tool controller that continuously determines the transfer function of a machine tool and uses the transfer function information in a manner that optimizes the cutting speed of the machine tool while maintaining the cutting path within a preset tolerance of the centerline of the desired cutting path.